Fig. 2: Analysis of ¹³C DQ–SQ solid-state NMR spectrum of ¹³C, ¹⁵N cysteine-labeled U32SecM.

a Cysteine C_α–C_β cross peak regions of the ¹³C DQ–SQ spectrum of ¹³C, ¹⁵N cysteine-labeled U32SecM cryo-EM sample (3.4 nmol). b C_α and C_β chemical shifts from U32SecM compared to values derived from a chemical shift database²⁴ (left panel). Ellipses contain 90% of the corresponding chemical shifts within each group²⁴ (H = helix, B = β-strand, C = coil). The spectral region for oxidized C_β cysteines in light gray, and for reduced cysteine in dark gray. c Relative integration ratio (Rel. Int. Ratio) of oxidized (light gray) or reduced residues (dark gray) or the overlapping region (white), which does not allow for differentiation, of one U32SecM sample. Signal intensity of oxidized cysteine residues (>35 ppm), reduced cysteine residues (<32 ppm), and the overlapping region (35–32 ppm) was divided by the total signal intensity of C_β chemical shifts. Error bars represent the standard error of the mean and were calculated using four different integration regions (“Methods”). Each circle represents the Rel. Int. Ratio of one individual integration region.